Production of aromatic hydrocarbons from petroleum



Jan. 8, 1946. E. R. LEWIS ET Al.

PRODUCTION OF AROMATIC HYDROCARBONS FROM PETROLEUM Filed June 12, 1941 #WL tui v s a N Q I which it is carriedout will description when readwith v.

Patented Jan. 8, 1946 I PRODUCTION OF AROMATIC HYDROCAR- BONS FROM PETROLEUM Elton R. Lewis, Roselle Park, and Chester L.

Read, Westfield, N. J., asslgnors, by mesne assignments, to Standard Catalytic Company, a

corporation of Delaware Application June 12, 1941, Serial No. 397,668 9 Claims. (Cl. 26o-668) This invention relates to the production of aromatic hydrocarbons of the type of benzene, toluene and mixed xylenes from petroleum and is more particularly concerned with an improved process by means of which substantially greater yields of these desired aromatic hydrocarbons may be obtained than have heretofore been considered possible.

Virgin fractions obtained from certain crudes are known to contain relatively small quantities of benzene and toluene. Ordinarily, these quantities are so small that attempts to isolate the benzene and toluene in substantially pure form are hardly worthwhile.

Recently a process has been developed according to which virgin petroleum fractions of narrow boiling range which are rich in cyclohexane, methylcyclohexane and dimethylcyclohexanes are subjected to catalytic reforming or catalytic de. hydrogenation whereby from 80 to 90% of the cyclohexanes are converted to the corresponding aromatics. In this way, the quantity of benzene, toluene or mixed xylenes may be increased to about l to 25% by volume based on the initial petroleum fraction. Following this treatment, the aromatics are recovered in substantially pure form by special types of solvent extraction.

We have now found that substantialv quantities of aromatics of the type of benzene, toluene and mixed xylenes and also cyclohexanes, and ethylcyclohexane may be vobtained by subjecting subsequent catalytic reforming or dehydrogenation of the destructively hydrogenated product the aromatic hydrocarbons remain substantially unchanged whereas the cyclohexanes converted to the corresponding aromatics.

Accordingly, the present invention has object the provision of a process by means of which the cyclohexanes normally present in petroleum together lwith may be formed byv destructive hydrogenation are subjected to catalytic reforming and the product cyclohexane and dey rvatives such as methylcyclohexane, dimethyl-'71,

distillate petroleum tra@ IA tions to destructive hydrogenation and that upon j those .cyclohexanes which For convenience in description it will be assumed that it is desired to produce substantially pure toluene. It should be understood however that the process is not limited to making toluene but is equally applicable to the production of benzene and mixed xylenes.

Referring to the drawing, numeral I designates a supply of a petroleumY fraction boiling between the approximate limits of 100 and 500 F. Pump 2 draws oil from tank I through line 3 and forces it through line 4 into a fractionating means 5. A fraction comprising hydrocarbons boiling below about 200 F. is removed from the top of the fractionating means through line 6. A fraction comprising hydrocarbons boiling above about 450 F. is removed from the bottom of the fractionating means through line 1. Two sidestreams are taken oil` from the center portions of the fractionating means, one comprising hydrocarbons boiling between about 200 and 250 F. being removed through line 8 and collected in tank 9, and a second comprising hydrocarbons boiling between about 250 and 450 F. being removed through line I0 and collected in a tank I I.

.The fraction boilingvbetween 250 and 450 F.-

is withdrawn from tank II through line I2 by Y means of pump I3 and forced through line Il into andthrough a heating means I5. Hydrogen or a gasrich in free hydrogen is supplied to line I4 through line I6 so that a mixture of oil and hydrogen `will flow through the heating "means I5. Ther heated mixture of oil and hydrogen iiows through line I1 into a reaction zone lf'which is adapted for high pressure destructive hydrogenation and `contains a catalytic material `I9`vvvhich promotes hydrogenation.

. @Reaction zone I8 is maintained under a presare largely?l pressure between: 50 and 300 atmospheres or :surei'n excessof 20 atmospheres preferably at @j Y, v -morefand ata. temperature between 600 and 950 yF. The oil is passed'through the reaction zone at"a 1rate betweeniofand 3.0 volumes of liquid of catalytic reforming is subjected to solvent ex-` ,l

traction for the recovery of stantially pure aromatics-; p y f The nature of the'process and they manner in be fully understood from the following fhigh yields ofj-sub;

`g oil-per volumeof catalystper hourv and the quan- .i-titygof hydrogen which `accompanies the oilis 1 between'kl000 land 15,000 cubic feet per barrel 'of oil. -The catalystjl may be selected Ifrom a great varietyof differentmaterialswhich promote hydrogenation. By way of example may be men-r tioned'oxides or sulfldes of metals of the VI. group ofgthe 'periodic system either alone or together Y i l oxides'lofj metals of theV 11 and Iv groups .of the periodic system. Mixtures of molybdenum oxide, chromium oxide and zinc oxide; tungsten v-sulde and nickel'suliide or molybdenum 'disulf alone particularly suitable.

Products oi' the destructive hydrogenatlon are removed from reaction zone I8 through 1ine20, passed through a cooling means 2l and then discharged through line 22 into a separating means means S in line 24 in order to remove at leastv a portion of the hydrocarbon constituents from the gases and thereby to increase theconcentration of hydrogen in said gases. i

Liquid products are removed from separating means 23 through line 26, pass through a pressure release valve 26aA and are returned to line 4 and fractionating means by means of pump 21. A fraction boiling between 200 and 250 F. is thus segregated-from the liquid products of destructive hydrogenation for further treatmentas will presently be described. Another fraction boiling betweenV 250 and 450 F. is also segregated and is returned to the destructive hydrogenation' for further treatment.

Returning to tank 9 the fraction boiling between 200 and 250 F., which consists of hydrocarbons separated directly from the initial oil and hydrocarbons separated from the product of the destructive hydrogenation or the 250 'to 450 F. fraction of the initial oil. is removed from tank 9 through line 30 by means of pump 3| and forced through line 32 into a heating means 33. Hydrogen or a gas rich in free hydrogen is also introduced into line 32 through line 34. As will be explained below, it is only necessary to supply hydrogen through line 34 when starting up the process about to be carried out in the absence of a supply of hydrogen previously generated in and accumulated from said process.

'I'he mixture of oil and hydrogen heating means 33 ows through line 35 into a reaction zone 36 which contains a catalytic material 31 which promotes catalytic reforming or dehydrogenation;

In reaction zone 36 the fraction boiling between 200 and 250 F. is subjected to catalytic reforming for the principal purpose oi.' converting the methylcyclohexane to toluene. Reaction zone 36 is maintained at a temperature between 850and 1050 F. and under a pressure between slightly above atmospheric and about 500 pounds per square inch, preferably between 50 and 400 pounds per square inch. The oil is passed through reaction zone 36 at a rate between 0.3 and 3.0 volumes oi' liquid oil per volume of catalyst per hour, and the quantity of gas containing hydrogen recirculated with the oil is between 1000 and 5000 cubic feet per barrelof oil. This gas should lcontain between 30 and 9 0 mol percent of free hydrogen and it will be understood that the larger volumes of gas will be used with the lower concentrations of hydrogen 'therein and vice versa. The catalytic material 31 in reaction zone, may consist of a major amount of aluminum oxide in any of its various forms together with a minor amount of an oxide or sulilde of a metal oi' the II, IV, V. VI or VIII groups of the periodic system. Suitable catalysts of this type comprise alumina gel, activated alumina, peptized alumina gel and peptized aluminum hydrates impreg- 'means 4l through line 42 and are recycled directly to line 32. A booster compressor 43 is provided in line 42.

Liquid products are removed from separating means 4l through line 44 and introduced into a fractionating means 45 wherein fractions boiling below 200 F. and above 250 F. are separated from the fraction boiling between 200 and 250 F.A The lower boiling and higher boiling fractions are removed from fractionating means 45 through lines 46 and 41 respectively. 'Ihe 200-250 F. fraction is removed from fractionating means 45 through line 48 and introduced yinto the bottom portion of a tower 49 adapted forl the countercurrent iiow of two liquids.

Numeral 50 designates a supply tank of a selective solvent which has preferential selective solvent power for aromatic hydrocarbons' under conditions at which it has relatively little solvent power for non-aromatic hydrocarbons. Examples of this type of solvent are liquid sulfur dioxide, phenol, cresol, cresylic acid, beta beta dichlorethyl ether, furfural, aniline and the like. Solvent islwithdrawn from tank 50 through line 5| by means of pump 52 and forced through line 53 into the upper portion of the tower 49 wherein it ilows downwardly in countercurrent to the upwardly rising hydrocarbon fraction. The preferred solvent for this purpose is liquid sulfur dioxide. It is used'in quantities of 60 to 300% of the volume of the hydrocarbon oil to be extracted and especially good results are obtained if the extraction is carried out at a temperature below 0 F., say between -20 and 60 F. or lower.

In tower 49 the liquid sulfur dioxide and oil 53 which supplies solvent to tower 49.

'I'he primary extract phase which will consist of most ofy the liquid sulfur dioxide and the aromatics but will also contain small amountsof non-aromatic hydrocarbons is removed from tower 49 through line 55 and introduced into the upper portion of a second tower 56 which is also preferably maintained kat a temperature below 0 F. wherein it iiows in countercurrent relationship to a non-aromatic hydrocarbon diluent which of the aromatics.

is supplied to the bottom portion of the tower through line 5l. The non-aromatic hydrocarbon diluent should be a highly paraflinic hydrocarbon oil having a boiling yrange substantially different Ifrom that of the aromatics and the liquid sulfur dioxide. This diluent may have a boiling range either higher or lower than that Examples of a lower boiling diluent vare pentane and iso-pentane. Examples of a higher boiling diluent are a. paraiiinic'heavy naphtha and a light kerosene. Fork purposes ot description, it will be assumed that the non-aroof the mechanisml of the reactions nor by anyl .y details which have been given merely for purposes of illustration but is limited only ln andby `the following claims in which it is intended to claim all novelty inherent in the invention. I

We claim:

l. An improved process lfor obtaining high yields of substantially pure aromatic hydrocarbons of the type of benzene, toluene and mixed xylenes from a petroleum fraction which comprises separating from said petroleum fraction a fraction containing cyclohexanes which correspond to the aromatic it is desired to obtain, segregating from said petroleum fraction another-fraction ofhigher boiling range than the first fraction separated, subjecting the higher boilingof the two fractions to destructive hydrogenation, segregating from the products of destructive hydrogenation a fraction of approximately the same boiling range as the rst fraction separated from the initial petroleum fraction, subjecting the two fractions of the same boiling range, one obtained directly from the initial petroleum fraction and theother obtained from the products of destructive hydrogenation, to catalytic reforming, separating from the products of catalytic reforming a fraction of narrow boiling range which contains the l desired aromatic, and recovering the desired aromatic from this narrow boiling fraction by solvent extraction.

2. Process according to claim l in which the narrow boiling fraction separated from the products of catalytic reforming is first extracted with liquid sulfur dioxide at a temperature below F. whereby a primary raiiinate. and a primary extract phase are obtained, countercurrently washf ing the primary extract phase with a non-aro matic hydrocarbon diluent having a boiling ra'nge substantially different from the hydrocarbons and liquid sulfur dioxide present in the primary extract phase whereby a secondary raffinate and a secondary extract phase are obtained, removing theliquid sulfur dioxide from the secondary extract phase and recovering substantially purek aromatic of the type desired from the solventfree secondary extract phase by fractionation.

3. Process according to claim 1 in which the narrow boiling fraction separated from the products of catalytic reforming is extracted in vapor A phase with a liquid solvent of substantially higher boiling point characterized by the fact that it depresses the vapor pressure of aromatic hydrocarbons to a greater extent than it does that of nonaromatic hydrocarbons.

4. Process according to claim 1 in which the catalytic reforming is conducted in the presence of hydrogen for a time and under such conditions that there is an overall net production of free hydrogen.

5. An improved process for obtaining high yields of substantially pure toluene from a petroassaut l leum fraction which comprises segregating from saidy petroleum fraction two fractions of narrow boiling range, one boiling between about 200 and 250 F. and the other boiling between about 250 and 450 F., subjecting the fraction boiling between 250 and 450 F. to destructive hydrogenation, segregating from the products of destructive hydrogenation a fraction boiling between 200 and 250 F., combining the two fractions boiling between 200 and 250 F., subjecting these to cataLvtic reforming, segregating from the products of catalytic reforming a fraction boiling between 200 andl 250 F., subjecting this last-mentioned fraction to extraction with liquid sulfur dioxide, and recovering substantially pure toluene from the extract phase so obtained. y

6. Process according toyclaim 5 in which the fractions of the products of destructive hydrogenation boiling between '250 and 450 F. are recycled to the destructive hydrogenation.

7. Processaccording to claim 5 in which the fraction boiling between 200 and 250 F. which is separated from the products of catalytic reforming is extracted with liquid sulfur dioxide ata temperature below 0 F. whereby a primary raillnate and a. primary extract phase are obtained, the primary extract phase is countercurrently washed with a non-aromatic hydrocarbon diluent of a boiling range different from that of the hydrocarbons and the liquid sulfur dioxide in-the primary extract phase whereby a secondary railinate and a secondary extract phase are obtained, the liquid sulfur dioxide is removed from the secondary extract phase and substantially pure toluene is recovered from the solvent-free secondary extract phase by fractionation.

8. Process according to claim 5 in which the catalytic reforming is conducted in the presence of hydrogen for a time and under such conditions that there is an overall net production of free hydrogen.

9. An improved process for obtaining high yields of substantiallyv pure toluene from a petroleum fraction which comprises segregating from said petroleum fraction two fractions of narrow boil'- ing range, one boiling between about 200 and 250 F. and the other boiling between about 250 and 450 F., subjecting the fraction boiling between 250 and 450 F. to destructive hydrogenation, segregating from the products of destructive hydrogenation 'a fraction boiling between 200 and 250 F., combining the two fractions boiling between 200 and 250 F., subjecting these to catalytic reforming, segregating from the products of catalytic reforming a fraction boiling between 200 and 250 F., subjecting this last-mentioned fraction in vapor phase to extraction with liquid phenol, and recovering substantially pure toluene from the extract phase so obtained.

ELTON R. LEWIS. 

